Fuel injection device

ABSTRACT

A fuel device including a high-pressure fuel source from which fuel is supplied to fuel injection valves. The fuel injection valves are controlled with the aid of a valve that is driven by a piezoelectric or magnetostrictive drive mechanism. With the aid of this drive mechanism, a 3-way valve having a closing body can be adjusted in an intermediary position in which a control chamber, by way of which a hydraulic force can be exerted in the closing direction on a valve closing member of the injection valve, can simultaneously be connected to a high-pressure fuel source and a relief chamber in order to adjust a control pressure that lies between the high pressure of the high-pressure source and a relief pressure. In this manner, a partial opening of the injection valve member of the injection valve can be adjusted in order to introduce a reduced injection quantity into the combustion chamber of the internal combustion engine.

PRIOR ART

The invention is based on a fuel injection device for a vehicle. In afuel injection device of this kind, which has been disclosed by DE 44 06901, a 3-way valve is used, which allows the control chamber tocommunicate either exclusively with the high-pressure fuel source orexclusively with a fuel return container. The actuation of the valvemember of this 3-way valve is executed with the aid of an electromagnet.With this known embodiment, the injection valve member is brought eitherinto a completely open position or into a completely closed position,depending on the triggering of the 3-way valve.

ADVANTAGES OF THE INVENTION

The fuel injection device according to the invention has an advantageover the prior art that the valve body of the valve member can bebrought into an intermediary position so that through the correspondingcontrol of the simultaneously existing connection to the high-pressurefuel source on the one hand and to the relief chamber on the other, thecontrol chamber has a lower or higher pressure than if the controlchamber were to be connected exclusively to one or the other of thepressure levels. Consequently, the injection valve member can alsoassume an intermediary position corresponding to a partial opening,which permits the valve member to produce a reduced injection rate offuel into the combustion chamber in this position. A 3-way valve of thetype defined can thus be used to advantageously produce a pre-injectionthat typically requires only a very small injection quantity. Throughthe partial excitation of the piezoelectric element or of themagnetostrictive element, the valve member executes a partial path andstays in a position between the two valve seats. Then, the valve membercan be brought back into a position pushing against the control chamberin order to interrupt the fuel injection between a pre-injection and amain injection in order to be finally brought into a position thatcompletely shuts off the inflow conduit, which leads to the discharge ofthe control chamber and produces the main injection that follows thepre-injection.

Accordingly, the tappet that actuates the valve body of the valve memberis advantageously connected to this valve body. In order to adjust therelief dynamics, a throttle is advantageously disposed in the outflowconduit.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of the invention is shown in the drawings andwill be explained in more detail in the description below.

FIG. 1 is a schematic representation of the fuel injection device,

FIG. 2 is a sectional view of a fuel injection valve of the fuelinjection device,

FIG. 3 shows the valve member that controls the fuel injection device,and

FIG. 4 shows a pressure progression that clarifies the triggering andthe effects of the control events of the 3-way valve.

DETAILED DESCRIPTION

The invention is based on a fuel injection device that has ahigh-pressure fuel pump 5, which obtains fuel from a fuel tank 6, ifneed be with the interposition of a pre-feed pump, and supplies the fuelat high pressure by way of a pressure line 7 to a high-pressure fuelreservoir 8. These parts are referred to as the high-pressure fuelsource. In order to control the pressure in the high-pressure fuelreservoir 8, a relief line 12 is provided, which contains a pressurecontrol valve 11 and leads from the high-pressure fuel reservoir back tothe fuel tank 6. By way of fuel lines 15, the high-pressure fuelreservoir 8 supplies each fuel injection valve 14 with fuel, which hasbeen brought to fuel injection pressure. These fuel injection valves areelectrically controlled by a control device 18, which controls theopening of the fuel injection valves 14 in accordance with operatingparameters of the internal combustion engine and thus determines theonset and duration of fuel injection. This control device alsosimultaneously controls the pressure control valve, wherein the pressurein the high-pressure fuel reservoir is detected as a parameter by meansof a pressure sensor 9 and is supplied to the control device.

FIG. 2 shows parts of a fuel injection valve 14 in a sectional view.This valve has a housing 19 in which a needle-like injection valvemember 21 is guided in a longitudinal bore 20. On its one end, thisinjection valve member is provided with a conical sealing face 23, whichcooperates with a seat on the tip 24 of the valve housing that protrudesinto the combustion chamber of the internal combustion engine, andinjection openings 25 lead from this seat and connect the interior ofthe fuel injection valve, in this instance the annular chamber 27 whichencompasses the injection valve member 21 and is filled with fuel atinjection pressure, to the combustion chamber in order to thus executean injection when the injection valve member has lifted up from itsseat. The annular chamber 27 is connected to a pressure chamber 29 thatcontinuously communicates with a pressure line 30, which is connected tothe fuel line 15 of the respective fuel injection valve. The fuelpressure thus supplied to the high-pressure fuel reservoir 8 alsoprevails in the pressure chamber 29 and acts on a pressure shoulder 31there by way of which the fuel injection valve member can be lifted upin a known manner from its valve seat under suitable conditions. On theother end of the injection valve member, the valve member is guided in acylinder bore 33 and encloses a control chamber 36 there with its endface 34. The closed position of the injection valve member is controlledby means of the pressure in the control chamber 36 and also by means ofa compression spring that is only depicted symbolically here by means ofan arrow F acting in the closed direction. Whereas the spring F thatacts in the closing force does not change in its characteristic curve,the opening and closing motion of the injection valve member istriggered with the aid of the pressure in the control chamber 36. Tothat end, the control chamber 36 is connected by way of a conduit 37 toa valve 40 that is embodied as a 3-way valve. This valve is shown inmore detail in FIG. 3. In this instance, the conduit 37 feeds from thecontrol chamber (36) into a valve chamber 41 in which a closing body 42of the valve member 43 of the valve 40 is movably disposed. To that end,the valve member 43 has a tappet 45 that is connected to the closingbody 42. A first sealing face 46 is disposed on the one end face of theclosing body and the second sealing face 47 is disposed on its other endface. The second sealing face transitions into a connecting piece 48 tothe tappet, which has a smaller diameter than the rest of the tappet 45,which is guided in a guide bore 50. An annular chamber 51, which is fedby an inflow conduit 53 is formed between the guide bore and theconnecting part 48 of the tappet 45. The annular chamber 51 constitutesa through flow conduit between the inflow conduit and the valve chamber41. At the discharge of the guide bore 50 into the valve chamber 41, avalve seat 54 is embodied, which as a second valve seat, cooperates withthe second sealing face 47. Coaxial to this and coaxial to the valvemember 43 or to the closing member 42, on the opposite end of the valvechamber 41, a first valve seat 55 is embodied, which cooperates with thefirst sealing face 46. Starting from the valve seat 55, an outflowconduit 57 leads from the valve chamber 41. This is likewise representedin FIG. 2 and leads back to the fuel tank 6 or to an otherwise embodiedrelief chamber. A throttle 58 is provided in the outflow conduit, whichdetermines the outflow cross section when the valve body is lifted upfrom the first valve seat 55. The inflow conduit 53, which can also beseen in FIG. 2, is connected to the fuel line 15 and can consequentlysupply fuel from the high-pressure fuel reservoir to the control chamber36 by way of the valve chamber 41 when the valve member 43 is lifted upfrom the second valve seat 54.

The first and the second sealing face 46 and 47, respectively, areembodied as conical in the current instance. The actuation of the valvemember 43 is carried out via the tappet 45 by a drive mechanism 59, notshown in detail, which is embodied as a piezoelectric device, e.g. as aso-called piezoelectric stack or as a magnetostrictive element. Thesedrive mechanisms have the advantage that they execute adjustment pathsthat are analogous to the voltage application and actually with a higheractuation force when the absolutely produceable path is also relativelysmall so that with large adjustment paths, large piezoelectric elementpackets must also be used. The additional advantage of drive mechanismsof this kind is comprised in that they act very quickly so that quickswitching events can be executed, which are highly advantageous,particularly in injection technology.

The valve body 42 can now be adjusted by the drive mechanism 59 so thaton the one hand, it comes into contact with its first sealing face 46against the first valve seat 55 and consequently shuts off theconnection between the control chamber 36 and the outflow conduit 57. Inthis instance, the high pressure of the high-pressure fuel reservoir 5is supplied to the control chamber 36 and due to the resultant forcefrom the pressure acting on the end face 34, of the valve member theinjection valve member 21 is held in the closed position. In anotherswitching state of the drive mechanism 59, the valve body 42 comes withthe second sealing face 47 of the valve body 42 into contact with thesecond valve seat 54 and consequently closes off the flow ofhigh-pressure fuel to the control chamber 36 and simultaneously opensthe outflow conduit 57. The control chamber 36 is then relieved and theinjection valve member 21 can travel into the open position as a resultof the high fuel pressure acting on its pressure shoulder 31 andconsequently, can execute a fuel injection. If the control chamber 36fills once more with high fuel pressure, the injection valve member 21is brought back into the closed position because of the now preponderantforce in the closing direction.

In lieu of the above-depicted positions of the closing body 42, thisbody can now be brought into an intermediary position by means ofcorresponding excitation of the piezoelectric elements of the drivemechanism 59 so that an average pressure between the highest pressurelevel corresponding to the pressure in the high-pressure fuel reservoirand the lowest pressure level corresponding to the relief pressure canbe adjusted in the control chamber 36. In accordance with the otherforces acting on the injection valve member, this produces thepossibility of bringing the injection valve member into an intermediaryposition via which fuel arrives at injection into the combustion chamberin a throttled fashion. This injection is preferably used for apre-injection of the kind that is required for noise reduction inengines with externally supplied ignition. At the top in FIG. 4, thepressure progression of the pressure P in the control chamber 36 isdepicted over time and beneath it is shown the stroke of the injectionvalve member, which corresponds in quantity and duration to therespective injection. It is clear that for the main injection H in thesolid lines at the top, the control chamber 37 is relieved to asignificantly greater degree than in the region of the pre-injection V.

For example, the throttle 58 is provided in the outlet conduit 57 inorder to dynamically influence the opening and closing movements of theinjection valve member 21. Furthermore, a throttle 60 can likewise beinserted in the inlet conduit 53 and influences the pressure increase inthe control chamber, wherein both throttles 58 and 60 are tuned togetherto the state of the intermediary position of the valve body between thetwo valve seats and the pressure production in the control chamber 36.These throttles and/or the respective proximity of the closing body 42to the one or the other of the valve seats 54 or 55 have an influence onthe resultant pressure of the control of the pre-injection quantity. Inthe example shown here, the inlet conduit 53 feeds into the annularchamber 51. In the reverse, the inlet conduit can also be disposed atthe location of the outlet conduit 57 of FIG. 3 and the outlet conduitcan be provided at the location of the inlet conduit 53 of this FIG. Onthe one hand, this embodiment has the advantage that in the region ofthe guidance between the guide bore 50 and the tappet 45, only low fuelpressures prevail so that a leak is prevented here. On the other hand,though, in the closed position of the sealing face 46 disposed on thefirst valve seat 54, a relatively higher pressure still acts on theremaining area on the valve body, which loads this valve body inopposition to the drive mechanism. This loading, however, can beovercome with the aid of piezoelectric elements which produce powerfulforces.

The foregoing relates to a preferred exemplary embodiment of theinvention, it being understood that other variants and embodimentsthereof are possible within the spirit and scope of the invention, thelatter being defined by the appended claims.

We claim:
 1. A fuel injection device for internal combustion engines,comprising a high-pressure fuel source (5, 8) that is connected to afuel injection valve (14), said fuel injection valve has an injectionvalve member (21) for controlling an injection opening (25) and has acontrol chamber (36), said control chamber is defined by a movable wall(34) which is at least indirectly connected to the fuel injection valvemember (21), and with an inlet conduit (53) through which fuel from ahigh-pressure source (8) communicates with the control chamber (36), andwith an outflow conduit (57) by way of which the control chamber (36) isconnected to a relief chamber (6), wherein the above-mentionedconnections to and from the control chamber are controlled by way of avalve (40), which has a valve member (43) with a closing body (42) thatis disposed so that the closing body moves coaxial to first and secondvalve seats (54, 55) in a valve chamber (41), the valve chambercontinuously communicates with the control chamber (36) by way of aconduit (37) and with a tappet (45) that is moved by an electricallyactuated drive mechanism (59), by means of the drive mechanism theclosing body (42) is moved between the first and second valve seats (54,55) and is guided in a guide bore (50) that coaxially adjoins one of thefirst and second valve seats (54, 55), wherein between the first valveseat (54), the tappet (45, 48) and the guide bore (50), a through flowconduit (51) is embodied in the housing (19) of the valve and isconnected to the outflow or inflow conduit and, adjacent to the secondvalve seat (55), the inflow or outflow conduit continues coaxially, anda throttle (58, 60) that controls the through flow is disposed in atleast one of the conduits (53, 57), a piezoelectric element or amagnetostrictive element is provided as the drive mechanism (59) of thetappet (45), of the drive mechanism excitation can be controlled so thatthe valve body (42) assumes a position in which one of the first andsecond valve seats (54, 55) is completely opened or completely closed,or assumes an intermediary position in which both of the valve seats(54, 55) are open in a controlled manner and the control chamber (36)experiences a partial relief by means of which the injection valvemember (21) is moved into a partially open position.
 2. A fuel injectiondevice according to claim 1, in which the tappet is connected to theclosing body.
 3. A fuel injection device according to claim 1, in whicha first throttle (60) is disposed in the inflow conduit (53) and asecond throttle (58) is disposed in the outflow conduit (57).
 4. A fuelinjection device according to claim 1, in which the inflow conduit (53)feeds into a valve chamber (41) on the side of the tappet (45).